Patent GB-186141-A (GB)
Abstract: 186,141. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. June 20, 1921. Automatic exchange systems. - A subscriber calling a dead or ceased number is automatically connected to an attendant's circuit at the same or a distant exchange, all the apparatus individual to the dead line except the test contacts, being left unconnected. The invention is particularly applicable to a by path system of the kind described in Specifications 181,115, 181,116, 181,118, 181,119, and 181,120, in which the test of the wanted line is effected by apparatus different from that which effects the connection, the testing circuits being arranged numerically while the talking circuits need not be. Fig. 1 shows a system of this kind in, which calling lines are connected through trunks OT to an impulse responder R. which, responding to the hundreds, tens, and units digits, connects battery to one of the mark ing-wires, for example 831, to bring about the connection of the corresponding line to the trunk OT, after which the responder R is released. The marking-wires of dead numbers, for example 410, 421, 432, are connected at the distributing frame to a common " ceased number bar " CNB, connected by wire 23 to a relay JME, Fig. 2. which causes the connection of the calling trunk OT to one of the trunks E leading to an attendant's circuit. Each of the trunks OT, Fig. 2, may be con nected, as described in Specification 181,120, to a subscribers line S by sending three digits in the usual way, or to an idle line in the groups E or F by sending a single digit 9 or 0. A trunk OT is thus connected to an idle line in the group E, which may lead to attendants circuits in the same or a distant exchange, when the digit 9 is dialled, and when a dead number is called. In order to avoid intereference, due to to the accidental prolonged connection of the bar CNB to earth or battery, with the connection of a calling line to the group E by sending a single digit, the bar CNB is wired to a relay CNM, Fig. 3. If the bar CNB is earthed, the relav CNM is short-circuited and the wire, 23 and relay JME are unaffected. If the bar CNB is connected to battery for a prolonged period, the relay CNM causes a slow-acting relay CNMS to bring into circuit a thermal switch T which, after say ten seconds, energizes a relay CNMA to open circuit 23 and light a warning lamp. Fig. 4 shows the invention applied to a connector of ordinary kind, described in Specification 181,115, in which the terminals of dead numbers are connected to terminals A, B of a call-finder connected to an attendant's circuit. The test wipers t of the connector and the test terminals are divided as shown, the upper test terminal of dead lines being connected to the starting wire of the finders, and the, lower test terminal to negative potential. At the end of dialling, when the relay D deenergizes, if the upper test wiper engages the terminal of a dead line, circuit 16 maintains relay PM energized keeping the side switch in its second position and connecting busy tone to the calling line. The circuit 16 energizes a relay ST in an idle callfinder, which rotates until its test wiper T completes a circuit 21 to stop the finder and energizes a relav BBCO, which locks up. disconnects the busy tone, and completes the talking circuit 20 through to the attendant's circuit. If the finder has been taken into use by a first selector Si. relay FSCO energizes relay CO to extend the starting-circuit 16 to another finder.